1. Field of the Invention
The present invention relates to a shift register and a Liquid Crystal Display (LCD), and more particularly, to a shift register having simple circuit scheme capable of increasing lifetime of whole circuit and a related LCD.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2. FIG. 1 shows a circuit diagram of a shift register in the U.S. Pat. No. 5,410,583, and FIG. 2 shows a simplified timing diagram of each signal shown in FIG. 1. When the signal C3 is at high voltage level, the voltage source VDD will charge the node P2 so as to turn on the transistor 17 and the transistor 19 so as to perform a discharging operation on the output terminal and turn off the transistor 16. However, only when the input signal INPUT turned on the transistor 21, the voltage level of the node P2 is pulled to VSS, and the voltage level of the node P2 is maintained at high voltage level afterward. Thus, the duty of the node P2 is close to DC. In general, when the duty of the node P2 is closer to DC, the threshold voltage Vth of the TFT increases faster. When threshold voltage Vth increases too much, the circuit will be damaged.
Please refer to FIG. 3 and FIG. 4. FIG. 3 shows a circuit diagram of a shift register in the U.S. Patent publication No. 20060146978, and FIG. 4 shows a simplified timing diagram of each signal shown in FIG. 3. The U.S. Patent publication No. 20060146978 uses four group of clock signals and nine transistors T1, T2, T3, T4, T5, T6, T7, T8, and T9 to control the node Q and the node Qb, so as to let the voltage level of the node Qb has a periodical variation to solve the problem of the U.S. Pat. No. 5,410,583. However, the circuit diagram of the U.S. Patent publication No. 20060146978 is very complicated, and it is not easy to realize in practical, and it has risk of low yield.